The main objective of the proposed research is to provide insights into structural organization of the eukaryotic and prokaryotic chromatin. The work will consist of three different but mutually interdependent lines of research, namely: 1. Detailed structural analysis of sub-, mono- and oligonucleosomes from mild nuclease digests of chromatins from human, mouse and Drosophila cell lines using in particular, new electrophoretic methods of separation and analysis of deoxyribonucleoproteins recently developed by us (2,7). 2. Studies on the structure of the prokaryotic (E. coli) chromatin, in particular, studies on interactions between two specific histone-like proteins recently found by us (1,5) in the highly purified E. coli deoxyribonucleoprotein. In addition, a search for a possible nucleosomal organization of the E. coli chromatin will be carried out using nucleases as probes. 3. Studies on the structure of the SV40 viral minochromosome as a model of the cellular chromatin structure. In particular, we shall investigate the problem of relation between nucleosomes and base sequences in DNA (phase problem) and study the way of DNA folding in the minichromosome using new experimental approaches and the recently described by us (3,5) the compact form of the SV40 minichromosome as a starting material. The results of this studies will contribute to the understanding of both structure and functioning of eukaryotic and prokaryotic chromosomes of cellular and viral origin.